scholarly journals Inclusion flotation-driven channel segregation in solidifying steels

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
Dianzhong Li ◽  
Xing-Qiu Chen ◽  
Paixian Fu ◽  
Xiaoping Ma ◽  
Hongwei Liu ◽  
...  
Keyword(s):  
Mushy Zone ◽  
Volume Fraction ◽  
Density Contrast ◽  
Compositional Variation ◽  
Technological Breakthrough ◽  
Channel Segregation ◽  
Induced Flow ◽  
And Control ◽  
Severe Destruction

Abstract Channel segregation, which is featured by the strip-like shape with compositional variation in cast materials due to density contrast-induced flow during solidification, frequently causes the severe destruction of homogeneity and some fatal damage. An investigation of its mechanism sheds light on the understanding and control of the channel segregation formation in solidifying metals, such as steels. Until now, it still remains controversial what composes the density contrasts and, to what extent, how it affects channel segregation. Here we discover a new force of inclusion flotation that drives the occurrence of channel segregation. It originates from oxide-based inclusions (Al2O3/MnS) and their sufficient volume fraction-driven flotation becomes stronger than the traditionally recognized inter-dendritic thermosolutal buoyancy, inducing the destabilization of the mushy zone and dominating the formation of channels. This study uncovers the mystery of oxygen in steels, extends the classical macro-segregation theory and highlights a significant technological breakthrough to control macrosegregation.

Permeability in the Mushy Zone

2010 ◽  
Vol 649 ◽  
pp. 399-408 ◽  
Author(s):  
R.G. Erdmann ◽  
D.R. Poirier ◽  
A.G. Hendrick
Keyword(s):  
Mushy Zone ◽  
Volume Fraction ◽  
Primary Dendrite ◽  
Fluid Velocity ◽  
Interdendritic Liquid ◽  
Creeping Flow ◽  
Liquid Region ◽  
Local Volume ◽  
Local Volume Fraction ◽  
Deterministic Function

When modeled at macroscopic length scales, the complex dendritic network in the solid-plus-liquid region of a solidifying alloy (the “mushy zone”) has been modeled as a continuum based on the theory of porous media. The most important property of a porous medium is its permeability, which relates the macroscopic pressure gradient to the throughput of fluid flow. Knowledge of the permeability of the mushy zone as a function of the local volume-fraction of liquid and other morphological parameters is thus essential to successfully modeling the flow of interdendritic liquid during alloy solidification. In current continuum models, the permeability of the mushy zone is given as a deterministic function of (1) the local volume fraction of liquid and (2) a characteristic length scale such as the primary dendrite arm spacing or the reciprocal of the specific surface area of the solid-liquid interface. Here we first provide a broad overview of the experimental data, mesoscale numerical flow simulations, and resulting correlations for the deterministic permeability of both equiaxed and columnar mushy zones. A extended view of permeability in mushy zones which includes the stochastic nature of permeability is discussed. This viewpoint is the result of performing extensive numerical simulations of creeping flow through random microstructures. The permeabilities obtained from these simulations are random functions with spatial autocorrelation structures, and variations in the local permeability are shown to have dramatic effects on the flow patterns observed in such microstructures. Specifically, it is found that “lightning-like” patterns emerge in the fluid velocity and that the flows in such geometries are strongly sensitive to small variations in the solid structure. We conclude with a comparison of deterministic and stochastic permeabilities which suggests the importance of incorporating stochastic descriptions of the permeability of the mushy zone in solidification modeling.

scholarly journals Effects of vertebroplasty on endplate subsidence in elderly female spines

2015 ◽  
Vol 22 (3) ◽  
pp. 273-282 ◽  
Author(s):  
Srinidhi Nagaraja ◽  
Hassan K. Awada ◽  
Maureen L. Dreher ◽  
John T. Bouck ◽  
Shikha Gupta
Keyword(s):  
Bone Cement ◽  
Trabecular Bone ◽  
Volume Fraction ◽  
Micro Ct ◽  
Control Groups ◽  
Bone Volume Fraction ◽  
Elderly Female ◽  
Maximum Subsidence ◽  
And Control ◽  
Adjacent Vertebra

OBJECT The aim in this study was to quantify the effects of vertebroplasty on endplate subsidence in treated and adjacent vertebrae and their relationship to endplate thickness and underlying trabecular bone in elderly female spines. METHODS Vertebral compression fractures were created in female cadaveric (age range 51–88 years) thoracolumbar spine segments. Specimens were placed into either the control or vertebroplasty group (n = 9/group) such that bone mineral density, trabecular microarchitecture, and age were statistically similar between groups. For the vertebroplasty group, polymethylmethacrylate bone cement was injected into the fractured vertebral body under fluoroscopy. Cyclic compression (685–1370 N sinusoid) was performed on all spine segments for 115,000 cycles. Micro-CT scans were obtained before and after cyclic loading to quantify endplate subsidence. Maximum subsidence was compared between groups in the caudal endplate of the superior adjacent vertebra (SVcau); cranial (TVcra) and caudal (TVcau) endplates of the treated vertebra; and the cranial endplate of the inferior adjacent vertebra (IVcra). In addition, micro-CT images were used to quantify average endplate thickness and trabecular bone volume fraction. These parameters were then correlated with maximum endplate subsidence for each endplate. RESULTS The maximum subsidence in SVcau endplate for the vertebroplasty group (0.34 ± 0.58 mm) was significantly (p < 0.05) greater than for the control group (−0.13 ± 0.27 mm). Maximum subsidence in the TVcra, TVcau, and IVcra endplates were greater in the vertebroplasty group, but these differences were not significant (p > 0.16). Increased subsidence in the vertebroplasty group manifested locally in the anterior region of the SVcau endplate and in the posterior region of the TVcra and TVcau endplates (p < 0.10). Increased subsidence was observed in thinner endplates with lower trabecular bone volume fraction for both vertebroplasty and control groups (R2 correlation up to 62%). In the SVcau endplate specifically, these 2 covariates aided in understanding subsidence differences between vertebroplasty and control groups. CONCLUSIONS Bone cement injected during vertebroplasty alters local biomechanics in elderly female spines, resulting in increased endplate disruption in treated and superior adjacent vertebrae. More specifically, bone cement increases subsidence in the posterior regions of the treated endplates and the anterior region of the superior caudal endplate. This increased subsidence may be the initial mechanism leading to subsequent compression fractures after vertebroplasty, particularly in vertebrae superior to the treated level.

Experimental investigations on characteristics of boundary layer and control of transition on an airfoil by AC-DBD

2018 ◽  
Vol 32 (08) ◽  
pp. 1850108 ◽  
Author(s):  
Xi Geng ◽  
Zhiwei Shi ◽  
Keming Cheng ◽  
Hao Dong ◽  
Qun Zhao ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Boundary Layer Transition ◽  
Plasma Actuators ◽  
Experimental Investigations ◽  
Dbd Plasma ◽  
Layer Transition ◽  
Piv Measurement ◽  
Induced Flow ◽  
And Control

Plasma-based flow control is one of the most promising techniques for aerodynamic problems, such as delaying the boundary layer transition. The boundary layer’s characteristics induced by AC-DBD plasma actuators and applied by the actuators to delay the boundary layer transition on airfoil at Ma = 0.3 were experimentally investigated. The PIV measurement was used to study the boundary layer’s characteristics induced by the plasma actuators. The measurement plane, which was parallel to the surface of the actuators and 1 mm above the surface, was involved in the test, including the perpendicular plane. The instantaneous results showed that the induced flow field consisted of many small size unsteady vortices which were eliminated by the time average. The subsequent oil-film interferometry skin friction measurement was conducted on a NASA SC(2)-0712 airfoil at Ma = 0.3. The coefficient of skin friction demonstrates that the plasma actuators successfully delay the boundary layer transition and the efficiency is better at higher driven voltage.

scholarly journals Texture and Microstructure Development in Al2O3-Platelet Reinforced Ce-ZrO2/Al2O3 Laminates Produced by Centrifugal Consolidation

1995 ◽  
Vol 24 (1-3) ◽  
pp. 43-52 ◽  
Author(s):  
Ryan K. Roeder ◽  
Keith J. Bowman ◽  
Kevin P. Trumble
Keyword(s):  
Microstructural Evolution ◽  
Volume Fraction ◽  
Phase Segregation ◽  
Functionally Gradient ◽  
Property Evaluation ◽  
Quantitative Image ◽  
Microstructural Design ◽  
Efficient Packing ◽  
And Control ◽  
Platelet Content

A dispersed, low-solids-fraction suspension containing Ce-ZrO2, fine Al2O3 and 5 vol% Al2O3-platelets was segregated using centrifugal consolidation to produce functionally gradient laminates (FGLs). Platelet alignment facilitated efficient packing of highly anisometric platelets to high densities. The complexity and anisotropy of the microstructure warrants a quantitative analysis of the microstructural evolution prior to any property evaluation. Quantitative image analysis was used to examine changes in the volume fraction, dimensional anisotropy, and gradient of pores and platelets with sintering time. In all cases, special attention was given to the effects of texture during microstructural evolution. Platelet alignment enhanced densification via anisotropic shrinkage, overcoming constraint that otherwise inhibits densification in platelet-containing materials. Also, platelet alignment and microstructural design were used to initiate and control anisotropic grain growth. Platelet growth (at the expense of smaller particles of the same phase) during annealing promoted further phase segregation and produced higher platelet content composites consisting of larger platelets, without having to consolidate high contents of large platelets.

Modeling of Solidification and Filling of Thin-Section Castings

2005 ◽  
Author(s):  
Sergio D. Felicelli ◽  
David R. Poirier
Keyword(s):  
Mushy Zone ◽  
Volume Fraction ◽  
Fluid Model ◽  
Flow Behavior ◽  
Model Development ◽  
Element Model ◽  
Channel Length ◽  
Multicomponent Alloy ◽  
Radiation Boundary Conditions ◽  
Wide Range

A finite element model for simulating dendritic solidification of multicomponent-alloy castings is used to study the filling and solidification of castings of thin cross section. The model solves the conservation equations of mass, momentum, energy, and alloy components and couples the solution with the thermodynamic of the multicomponent alloy through a phase diagram equation. The transport of mass and energy in the mushy zone is done considering the mushy zone as a porous medium of variable porosity. The same set of conservations equations are used for the liquid, solid and mushy zones, in which the volume fraction of liquid acts as the variable that makes the equations transition continuously from one zone to another (Felicelli et al. [1]). During filling, the model tracks the advancing front as the metal flows into the thin mold, and solidification is calculated as the metal loses energy by convection and radiation to the mold, including the dynamic calculation of view factors. The code supports two fluid models that emulate the flow behavior under equiaxed or columnar solidification. In the former case a slurry fluid model is used in which the viscosity is determined by the volume fraction of solid. In this slurry state, the solid and liquid move at the same velocity. For the case of columnar solidification, the solid is fixed and the liquid flows through a porous structure of dendrictic solid. The model development is based on the work by Felicelli et al. [2], to which several features were added, including a front-tracking technique (Gao [3]) and thermal radiation boundary conditions. Calculations for Ni and Al alloys were performed to illustrate the effect of several physical and operation parameters in the filling of a horizontal channel of thin thickness. A wide range of process parameters was tested in order to determine how much of the channel length could be filled before blockage of flow by solidification occurred. In a separate section, the effect of alloy concentration on the fluidity was studied using a Pb-Sn hypoeutectic system, and the importance that the dendrite breaking phenomenon can have on the results is shown. Conclusions about the parameters that most influence the filling process are presented, as well as recommendations on which experimental data are more critical in order to conduct a proper validation of this type of models.

scholarly journals A Novel Transportation Method Based on Dynamic Control of Ripening Environment

2020 ◽  
Vol 13 (5) ◽  
pp. 58-66
Author(s):  
Xinyu Liu ◽  
◽  
Xiaojie Jin
Keyword(s):  
Low Temperature ◽  
Fruits And Vegetables ◽  
Control Method ◽  
Volume Fraction ◽  
Dynamic Control ◽  
Exogenous Ethylene ◽  
Quality Of Products ◽  
And Control ◽  
Air Circulation

The dynamic control of atmosphere is an important factor for guaranteeing the quality of climacteric products during transportation. As atmosphere changes, respiration climacteric products would rot because of overripeness, thus leading to loss. Moreover, climacteric products must be ripened artificially when delivered to the destination, thereby causing economic waste. In this study, a new transportation method based on dynamic control of ripening environment was designed.The ripeness control method based on the dynamic control of ripening atmosphere was presented to accomplish quality safety during transportation as well as avoid a subsequent extra process of ripening. The transportation method was employed to stem from the ethylene’s ripening effect on climacteric fruits and vegetables. The ethylene generator and air circulation unit, which dynamically regulate and control the dual regional atmosphere of carriages during transportation, were quantitatively controlled by the central treatment layer. Ripeness level could be regulated by controlling the temperatures and time of exogenous ethylene release, to control the quality of products and ripen them. The proposed method was proven feasible through experiments. Results demonstrate that a volume fraction of 0.01% exogenous ethylene allows bananas’ respiratory intensity to reach the peak early; meanwhile, moderate low temperature (16 °C) can enable ethylene peak to appear in advance. Therefore, bananas’ ripeness can be controlled by changing temperatures and the ripening environment when transporting. This study can provide references for the control of products’ ripeness during transportation.

scholarly journals Channel segregation during columnar solidification: Relation between mushy zone instability and mush permeability

2021 ◽  
Vol 164 ◽  
pp. 120602
Author(s):  
Alok Kumar ◽  
Miha Založnik ◽  
Hervé Combeau ◽  
Gérard Lesoult ◽  
Arvind Kumar
Keyword(s):  
Mushy Zone ◽  
Channel Segregation

Cervical sympathectomy and cerebral microvascular and blood flow responses to hypocapnic hypoxia

1989 ◽  
Vol 256 (2) ◽  
pp. H460-H467 ◽  
Author(s):  
I. Kissen ◽  
H. R. Weiss
Keyword(s):  
Blood Flow ◽  
Volume Fraction ◽  
Fluorescein Isothiocyanate ◽  
Brain Capillary ◽  
Hypoxic Conditions ◽  
Significant Difference ◽  
Microvascular Response ◽  
Fluorescein Isothiocyanate Dextran ◽  
And Control ◽  
Peripheral Sympathetic Nervous System

This study evaluated the effects of bilateral superior cervical ganglionectomy on cerebral blood flow (CBF) and utilization of brain capillary reserve in conscious rats during normoxia and hypoxia (8% O2 in N2). Regional CBF was determined in sham-lesioned and ganglionectomized rats with [14C]iodoantipyrine. The percentage of the total volume fraction and number of perfused capillaries was determined by comparing the perfused microvessels, identified by the presence of fluorescein isothiocyanate dextran, with the total microvascular bed, identified by alkaline phosphatase stain. There were no significant differences in regional CBF between control and ganglionectomized rats under normoxic conditions. CBF increased significantly during hypoxia in both control and control ganglionectomized rats. In control, hypoxic flow to caudal structures was significantly higher than to rostral structures and that differential response was prevented by ganglionectomy. There was no significant difference in the number of perfused microvessels between sham-lesioned and ganglionectomized rats during normoxia. The number of perfused arterioles and capillaries was significantly higher under hypoxic conditions than under normoxic conditions in sham and ganglionectomized animals. During hypoxia, the percent of arterioles per squared millimeter perfused increased to 63 +/- 5% in sham-lesioned rats and to a significantly greater extent, 80 +/- 6%, in ganglionectomized rats. The percentage of capillaries per squared millimeter perfused changed similarly. The peripheral sympathetic nervous system appeared to play an important role in the control of cerebral microvascular response to hypoxia.

Criterion for Dendrite Fragmentation of Steel under Imposition of Linear Traveling EMS

2010 ◽  
Vol 148-149 ◽  
pp. 84-91
Author(s):  
Jin Chen ◽  
Zhi-Jian Su ◽  
Keiji Nakajima ◽  
Ji Cheng He
Keyword(s):  
Fluid Flow ◽  
Mushy Zone ◽  
Volume Fraction ◽  
Critical Volume ◽  
Solute Content ◽  
Dendrite Fragmentation ◽  
Critical Volume Fraction

In the fragmentation theory of T. Campanella et al, the local remelting of dendrite arms is induced by the solute-rich fluid flow. Based on this theory, the effects of linear EMS intensity and solute content on CET of steel are investigated. The conclusions are as follows: The criterion for dendrite fragmentation under linear EMS is derived based on dendrite fragmentation theory by T. Campanella et al. And the criterion is verified with steel experiments. It is valid for steel under the Linear EMS. Investigation is carried out on relation between critical volume fraction of solid and solute content at the time of dendrite fragmentation (CET occurrence). It is concluded that critical volume fraction of solid is small with low EMS intensity and it decreases with the increase of solute content (C, Mn). The reason is that it causes that flow in the mushy zone becomes small which leads to CET occurrence difficult.

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